1. Field of the Invention
This invention relates generally to pavement markers, and is particularly concerned with pavement markers utilizing retro-directive reflecting elements for relfecting light from vehicles traveling over the roadway on which the pavement marker is mounted.
2. Description of the Prior Art
Roadway or pavement markers using reflectors having retro-directive reflector elements have come into widespread use to delineate traffic lanes and the edges of roadways. Such roadway markers are superior to painted strips on the roadways since under poor weather conditions, painted strips on the roadways are not visible.
The most common type of reflector utilized in such roadway markers are those formed with cube corner reflex reflector elements. Cube corner reflector elements have three planar surfaces arranged mutually at right angles with respect to each other, the three surfaces meeting at a common point or apex which is remote from the incident, light receiving surface of the reflector on which the reflector elements are formed. Light rays striking the incident, light receiving surface of the reflector are first refracted by the material of the reflector, and are then reflected by the cube corner reflector elements toward the source of the incident light rays. Before being reflected by the cube corner elements, the refracted incident light ray strikes each of the three cube corner surfaces, in almost every case, before the refracted light ray is reflected back toward the source. The three reflections on the cube corner surfaces increases the length of the light path in the material of the reflector, which, in turn causes more absorption of the light to reduce the amount of light reflected.
Examples of prior art pavement markers are reflectors are disclosed in U.S. Pat. Nos. 835,648; 2,172,660; 1,675,431; 2,330,096; 3,332,327; 3,541,606 and 3,784,279.